Well, maybe because gnutls26 is required but you installed gnutls28? If this isn't just a typo...

But I think it should build with gnutls30 also. There was a commit that addressed building with both gnutls26 and gnutls30 but linking against either of these at runtime.

That header is provided in proton.git/contrib/include. It is provided to Wine's configure with CFLAGS in the makefile. Are you using the makefile to build? Is your proton git branch up to date?

I am trying to use this branch https://github.com/jzengc/wine/tree/proton_3.16_mf

What should I change for this to work?

You need to build these Wine branches from within https://github.com/ValveSoftware/Proton/ . You can't build them stand-alone.

jzengc has an equivalent Proton git repository. In any case, issues with forks of Proton should be reported to the fork.

I am sorry about that, but I couldn't find Issue tab with the forks, so I didn't know where to report this issue.

Faced similar issue.

@ahmed-elsayed2017

What can I do to avoid this error?

Execute in an empty directory:

git init
git remote add proton git://github.com/ValveSoftware/Proton.git
git fetch --depth=1 proton proton_3.16
git checkout proton/proton_3.16 -- contrib

mkdir -p empty

diff -urN empty contrib > gnults26-include.patch

Then:

cd /your/wine/build
patch -p1 < /path/to/gnults26-include.patch

@aeikum

You can't build them stand-alone.

I have all required modules installed system-wide, except lsteamclient. If it possible to split lsteamclient into separate repo -- it would be great.
But despite that wine builds fine for me, w/ patch mentioned above.

@pchome @aeikum Yes, a split-out lsteamlib would be great... Could the subdir just be moved into its own repository? Or does it have deps across the subdir boundary (except wine itself)?

Building inside Proton makes a wine build that doesn't run.

Building with the patch @kakra mentioned gives the same with this error message at the end:
0009:err:module:load_library somehow failed to load steamclient

It is useless!